The original "builders of roads", the Ancients were once a race of advanced humans who were the original architects of the Stargate network. According to the Asgard, they moved on from our part of space long ago. In fact, the Ancients learned to ascend to a higher plane of existence when a great plague swept across the galaxy. Many died out, but those who learned to ascend shed their corporeal form gained a new sense of purpose.

The Ancients were once key members of an alliance of four great races in the galaxy, along with the Asgard, the Nox and the Furlings. The Ancients lived on Earth long ago -- or perhaps evolved on Earth itself, millions of years before our species did. One Ancient, Ayiana, was buried in ice in Antarctica for millions of years. Ayiana was left behind by the Ancients when they left Earth with the city of Atlantis, moving to the Pegasus Galaxy between five and 10 million years ago.

In Pegasus the Ancients seeded human life on many hundreds of worlds, as they had once done in our galaxy. They lived there for millions of years -- but then they came upon a planet where a powerful enemy slept. The Ancients had never before encountered a race with technology that rivaled their own. Awakened, the Wraith began feeding on the human-populated worlds, until only Atlantis remained untouched. The Wraith brought their powerful weapons to bear on the city, but the Ancients' shield held. Defeated, they submerged the great city into the ocean, and the last of them fled through the gate back to Earth. There they presumabley lived out their lives, telling stories that gave rise to the legend of the lost city. It is not known if these survivors ever ascended or had any contact with the ascended Ancients.

The Stargate network proves that the Ancients were one of the universe's most advanced species many millions of years ago, and had great minds into constructing a means to disperse many thousands of Stargates across the vastness of space -- even beyond our galaxy. They even had the technology to stop the movement of time itself (on several planets at once) and reverse it a number of hours, though they were unable to perfect that particular technology. Other advanced technologies left behind by the species include a device capable of altering human DNA to bring out advanced abilities, a healing device capable of restoring life and even animating non-living tissue, and more.

What is left of the Ancients, through gaining a higher moral center after ascension, is a hierarchy of somewhat omni-present, ethereal beings who feel they must remove themselves from interaction with all cultures beneath their non-corporeal plane. To merely interact with an individual beneath is breaking their law. Assisting a lower being in discovering ascension is punished by banishment. Meddling in circumstances that change the direction of a civilization is by far the most dire offense.

As punishment for breaking this law, the Ancients have been known to wipe out entire civilizations and abandon the one responsible in the midst of the mess they have caused. They have also forced (or tried to force) transgressors to descend back to corporeal form. Ancients are, by every means, capable of drastically altering courses of events at will. But, aside from their often cruel behavior, the Ancients do possess a high moral center that governs the majority's actions.

Ancients also have the ability to appear in human form or to reassume corporeal form permanently. Re-ascending then requires help from other Ancients.

Ascended beings have the ability to control weather conditions, turning a cloudless day into a hazardous lightning storm, and even using lightning as a weapon against enemies both in the air and on the ground.

Though the Ancients are not physically present, their actions have visibly altered the efforts of SG-1, among others. The Atlantis expedition is living in the Ancients' advanced city, which they were forced to abandon when the Wraith attacked thousands of years ago. Despite the fact that they are non-corporeal, they are still a powerful force to be reckoned with.

ALTERANS

A race of people who who originated in a distant galaxy and eventually travelled to the Milky Way Galaxy, where they became known as the Ancients. Many evolved to live on a higher plane of existence, and came to believe that they should not interfere with the lives of mortal beings.

The Alterans left some behind in their home galaxy, who also learned to ascend and became the Ori. The Ori took on an entirely different philosophy, believing they should be worshipped. They regarded the Alterans as evil, as those who abandoned the path of enlightenment -- and who kept the existence of human life in the Milky Way Galaxy a secret from them.

It is not clear whether or not the two groups were originally from the same species, the Alterans.